Volunteers are scouring the desert for Nancy Guthrie. Police want them to stop

The disappearance of Nancy Guthrie, mother of "Today" show host Savannah Guthrie, three weeks ago has prompted volunteers to launch their own searches in the dense desert near her home, hoping to uncover clues. Ms Guthrie, 84, was last seen at her residence just outside Tucson on 31 January and…